SUMMARY Gene therapy is a promising approach for the treatment of various monogenic diseases including inherited cardiomyopathies and other types of heart failure. Adeno-associated vectors (AAV) are vectors of choice for delivering genes to cardiomyocytes for long term expression and due to their safety in clinics. However, a significant challenge to their successful use is futility caused by pre-existing antibodies (NAbs) as well as subsequent development of immunity following AAV administration. NAbs prevent AAVs from infecting target cells, greatly reducing transduction efficiency, and thus, clinical efficacy. Therefore, to advance gene therapies for cardiovascular treatment for a wider population, it is essential to develop strategies to circumvent NAbs. Exosomes are extracellularly secreted nano-vesicles that shuttle selective biomolecules between neighboring and distant cells. Recent studies have shown that exosomes can carry several types viruses and shield them from antibody neutralization. Delivery of AAVs protected by carrier exosomes is a promising approach to circumvent NAb neutralization in AAV-based gene therapy. Our in vitro and in vivo preliminary data suggest that AAV-encapsulating exosomes (AAVExo) are 1) more resistant to NAb neutralization as compared to free AAVs, 2) more efficient in delivering genes to the myocardium, 3) preserves viral cardiotropism, and 4) retains the therapeutic benefits of AAV-mediated gene delivery. Here, we aim to investigate the ability of AAVExo to evade NAbs and serve as a highly efficient gene delivery tool for cardiovascular therapeutics. We have developed a method to isolate highly pure AAVExo with minimum contamination from free-AAVs. Our central hypothesis is that AAVExo shields AAVs to evade NAb and enhance gene delivery to the myocardium compared to free AAVs. Our major goal is to develop a comprehensive understanding of the molecular mechanisms of NAb neutralization by AAVExo, and 2) to determine the beneficial effects of therapeutic genes delivered by AAVExo in preclinical animal models of heart failure. The specific aims are: AIM 1: Characterize AAVExo and determine its gene delivery efficacy and molecular mechanisms of NAb evasion in vitro. AIM 2: Determine the gene delivery efficacy, cardiotropism and mechanisms of NAb evasion of AAVExo in vivo. AIM 3: Optimize AAVExo purification using a NanoDLD microfluidic device and determine the beneficial effect of AAVExo-SERCA2a in small and large animal models of heart failure with preexisting NAb.